1. Field of the Invention
The present invention relates to a fingerprint reading method and a fingerprint reading apparatus.
2. Description of the Related Art
Today, the authenticity of a person is often checked through fingerprint collation by using a fingerprint reading apparatus instead of using a password. An optical fingerprint reading apparatus converts the undulations of a fingerprint of a person into intensities of light, converts the intensities to an electric signal (image signal according to the fingerprint) by an image pickup unit, then compares the obtained with electric signal with the electric signal of that person that has been stored in advance to check if the person is authentic. To obtain a signal of a light intensity according to a fingerprint, a detection beam emitted from a light source is irradiated on a fingerprint collation surface against which a finger tip is pressed, and that detection beam which is reflected at the fingerprint collation surface or reflected light is input to the image pickup unit via an image forming lens or the like.
With such a fingerprint reading apparatus in use, there may be some people who attempt deceit of pressing false fingers, which have the fingerprints of other persons, against the fingerprint collation surface instead of pressing their genuine fingerprints. That is, there may be some people who try to practice deception to illegitimately pass as inauthentic persons though they are not. There are various false fingers conceivable. One example is a copied image of (the fingerprint at) the finger tip of an authentic person.
To prevent deception using such a false finger, a check is made to determine if a finger tip pressed against the fingerprint collation surface is a genuine one or determine the authenticity of the finger tip. One scheme of checking the authenticity of a finger tip is to discriminate whether an object pressed against the fingerprint collation surface is a living body or not (see, for example, Japanese Patent No. 2637253, Japanese Patent No. 2774313, Japanese Patent No. 277375 and Japanese Patent Laid-Open No. 2000-201907).
All the schemes described in those publications require that a separate special structure to detect a living body be added to an optical system which is needed for fingerprint collation. This requirement is an essential cause for the enlargement of fingerprint reading apparatuses and an increase in the cost thereof.